The present invention relates to vector particles intended for the specific delivery of biological material to cells.
For the correction by gene therapy of many inherited or acquired defects of the hematopoietic system, the therapeutic gene must be delivered to cells able both to self-renew and to differentiate into all hematopoietic lineages. As such, these gene therapies must be targeted to the “right” cells, i.e. hematopoietic stem cells (HSCs), without modifying their properties. The population of choice for targeting HSCs is constituted of CD34+ progenitor cells, which are particularly enriched in these stem cells. However, CD34+ cells only represent 0.001% of the total blood cells for instance. Accordingly, to avoid the cumbersome steps of cell extraction, culture in the presence of multiple growth factors or transduction adjuvants, and infusion into the patient, the vector particles have to display a very high specificity towards CD34+ cells, in order to allow transduction of CD34+ cells in non-purified bodily samples, such as blood samples, or to ensure an efficient in vivo transduction of CD34+ cells despite dilution of the vector particles.
Thus, Sandrin et al. (2002) Blood 100:823-832 have devised Simian Immunodeficiency Virus (SIV)-derived vector particles which display a chimeric envelope glycoprotein, RDTR, constituted of the fusion of the transmembrane and extracellular domains of the feline endogenous RD114 virus envelope glycoprotein and the cytoplasmic domain of the Murine Leukemia Virus-A envelope glycoprotein. Such vector particles are also disclosed in WO 03/91442. When using a transduction adjuvant, such as RETRONECTIN®, the transduction rate obtained using vector particles displaying the chimeric RDTR protein is of approximately the same rate as that observed with SIV-derived vector particles displaying the Vesicular Stomatitis Virus (VSV) G envelope glycoprotein. However, in the absence of transduction adjuvant, the RDTR vector particles exhibit a much lower transduction of isolated CD34+ cells than vectors displaying the VSV-G glycoprotein. Besides, no particular selectivity towards CD34+ cells has been shown to be associated to RDTR, since vector particles displaying this chimeric protein transduce CD34+ cells and peripheral blood lymphocytes with approximately the same efficiency.
In another attempt at targeting CD34+ cells, Verhoeyen et al. (2005) Blood 106:3386-3395 have devised HIV-1-derived vector particles which display the VSV-G envelope glycoprotein and so-called early acting cytokines, namely Thrombopoietin (TPO) and Stem Cell Factor (SCF). The authors have thus shown that these vector particles provided for efficient transduction of isolated CD34+ cells. However, no targeting specificity of these vector particles could be evidenced.
Accordingly, it is an object of the present invention to provide vector particles which are more efficient than those of the prior art at specifically targeting CD34+ cells.